Hello,
I'm having a problem with vibrations while driving. When the TC locks up into 4th gear (around 40 mph), the truck shakes vigorously. Then while giving it more gas to continue speed increase the vibration goes away after like 47-50 mph.

Anyone have any suggestions? I thought I read somewhere this could be a sign of bad injectors? I really dont know as I'm completely new to diesel and trying to learn quick

I should add that 1 was visibly bad, but the other one was not, only when removed and turned by hand. So you DO need to remove the drive shaft to check them. Make sure you mark the whole assembly (and block the wheels) so it is still aligned up the same when you re-assemble. Good time to grease the slip joint while you're in there.

after examining all the U-joints (all 3) they all look good. I suppose they could have gone bad on the inside? I also noticed they all have a fitting for grease, I guess I will add some grease to them all and see what happens. IF that doesnt work i guess I might have to replace all 3.

after examining all the U-joints (all 3) they all look good. I suppose they could have gone bad on the inside? I also noticed they all have a fitting for grease, I guess I will add some grease to them all and see what happens. Any advice?

Definitely won't hurt to lube them up.

Did you remove the shaft to check them? When I first started having issues, all my U-Joints looked fine. The vibration steadily got worse, then upon re-inspection I found one where the plastic seal was off, and there were only 2 needle bearings left, 1 of which fell out when I removed the shaft. the middle one looked fine but had almost no movement turning 1 way, which I'm sure contributed to the vibration.

My drive shaft was out of balance. Before it was like sitting in a massage chair between about 50 and 60 mph and severe enough the mirrors were almost useless. Just a thought if you don't find anything with the U-joints.

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